Solve for $x$ and $y$ using substitution. ${-x-3y = 1}$ ${x = 3y-7}$
Answer: Since $x$ has already been solved for, substitute $3y-7$ for $x$ in the first equation. ${-}{(3y-7)}{- 3y = 1}$ Simplify and solve for $y$ $-3y+7 - 3y = 1$ $-6y+7 = 1$ $-6y+7{-7} = 1{-7}$ $-6y = -6$ $\dfrac{-6y}{{-6}} = \dfrac{-6}{{-6}}$ ${y = 1}$ Now that you know ${y = 1}$ , plug it back into $\thinspace {x = 3y-7}\thinspace$ to find $x$ ${x = 3}{(1)}{ - 7}$ $x = 3 - 7$ ${x = -4}$ You can also plug ${y = 1}$ into $\thinspace {-x-3y = 1}\thinspace$ and get the same answer for $x$ : ${-x - 3}{(1)}{= 1}$ ${x = -4}$